The present invention relates to a method of manufacturing an electronic tube for a television or a computer.
Conventionally, a method of manufacturing an electronic tube described in the Japanese Patent Application Laid-Open No. 59-94325 is known.
The configuration of an electronic tube for a television or a computer is shown in FIG. 1. The reference number 1 denotes a shadow mask, 1a an electron gun side surface of the shadow mask, 2 an electron gun, 3 a fluorescent screen, 4 electron beam, and 5 an electronic tube.
The shadow mask 1 formed of metal material is provided with a plurality of round or rectangular apertures on the whole surface so that electrons are projected only to desired micropositions on the fluorescent screen 3.
Although electron beam 4 irradiated from the electron gun 2 is projected to the whole shadow mask 1, only electrons passing through said apertures of the shadow mask 1 reach the fluorescent screen 3 to form an image.
Since the number of electrons colliding against the shadow mask 1 is sometimes larger than that of electrons passing through the apertures of the shadow mask 1, however, the kinetic energy of the colliding electrons is converted into thermal energy to elevate temperature of the shadow mask 1 to about 70xc2x0 C. or higher.
Thermal expansion of the shadow mask 1 following said elevation in temperature causes dislocation of the apertures of the shadow mask 1 and thus changes the positions of electrons irradiated on the fluorescent screen 3, leading to distortion of an image. Such a change in beam position caused by thermal expansion of a whole shadow mask, which results from irradiation of electron beam from an electron gun contained in an electronic tube to the whole surface of a fluorescent screen, is called xe2x80x9cdoming.xe2x80x9d
According to the conventional method of manufacturing an electronic tube 5, since an appropriate amount of coating of a paint containing a metal element with an atomic number not lower than 70 is considered to be not lower than 0.2 mg/cm2 but not higher than 2 mg/cm2 in order to suppress this doming, bismuth oxide powder and the like having a large effect of reflecting electrons (hereinbelow, referred to as electron reflection effect) has been painted on the electron gun side surface 1a of the shadow mask.
The electron reflection effect is known to be related to the atomic number of a material and to increase as the atomic number increases.
When material with a high electron reflection effect, such as bismuth oxide, is painted on the electron gun side surface 1a of a shadow mask, conversion of kinetic energy of electrons into thermal energy is prevented, since projected electrons are reflected by the surface 1a and do not enter the shadow mask 1.
Consequently, an elevation in temperature of the shadow mask 1 is prevented so that doming caused by thermal expansion can be suppressed and a problem of image distortion be solved.
In the conventional method of manufacturing an electronic tube, paint containing a metal element with an atomic number not lower than 70 has been painted. The conventional method has, however, been suffered from such a problem, due to excessively high electron reflection effect, that electrons reflected on the electron gun side surface of a shadow mask scatter in the electronic tube and the scattered electrons are projected even to such areas of a fluorescent screen as requiring no electron projection, thereby deteriorating image quality.
In the conventional method of manufacturing an electronic tube, an appropriate amount of coating of a paint containing a metal element with an atomic number not lower than 70 is considered to be not lower than 0.2 mg/cm2 but not higher than 2 mg/cm2. However, since the amount of painting in this range is higher than required, there is such a problem that peeling of paint material from the surface of a shadow mask occurs in an electronic tube after the electronic tube is completed, causing pollution inside the electronic tube and resulting in deterioration of image quality.
An object of the present invention is to provide an excellent method of manufacturing an electronic tube by minimizing doming and solving the problem of deterioration of image quality.
In order to solve the above-mentioned problem, the present invention relating to a method of manufacturing an electronic tube provides a method of manufacturing an electronic tube in which an electron reflection coat is formed on the electron gun side surface of a shadow mask to an amount of coating of less than 2 mg/cm2 by painting a paint mainly comprising a solated metal oxide or a metal alkoxide of an element with an atomic number not lower than 40. By using the above-mentioned paint, including the case where an element with an atomic number not lower than 70 is used, an electron reflection effect becomes appropriate to provide a good image quality.
In addition, the paint comprising a metal element with an atomic number not lower than 40 is coated on the electron gun side surface of a shadow mask by a sputtering method or a vapor deposition method to achieve coating with an amount of coating of less than 0.2 mg/cm2, thereby to manufacture an electronic tube making a same effect as mentioned above.
The method of manufacturing an electronic tube according to the present invention can provide an electronic tube with less doming and good image quality.
The present invention will be now illustrated in more detail. According to the first aspect of the present invention, a method of manufacturing an electronic tube is provided which is characterized in that an electron reflection coat is formed on the electron gun side surface of the shadow mask to an amount of coating of less than 2 mg/cm2 by painting a paint mainly comprising a solated metal oxide of an element with an atomic number not lower than 40, said method giving an excellent image quality due to an appropriate electron reflection effect achieved by the paint comprising the metal oxide in a sol state. It is also characterized in that one of sodium silicate, potassium silicate, and lithium silicate or a mixture thereof is used as a binder and water is used as a solvent for the paint. It is also characterized in that the electron reflection coat may be formed by a spray method or a spin coating method.
According to the second aspect of the present invention, a method of manufacturing an electronic tube is provided which is characterized in that an electron reflection coat is formed on the electron gun side surface of a shadow mask to an amount of coating of less than 2 mg/cm2 by painting a paint mainly comprising a metal alkoxide of an element with an atomic number not lower than 40, said method achieving an effect similar to that mentioned above even using metal alkoxides. Similarly, it is also characterized in that an electron reflection coat may be formed by a spray method or a spin coating method.
According to the third aspect of the present invention, a method of manufacturing an electronic tube is provided which is characterized in that an electron reflection coat mainly comprising an element with an atomic number not lower than 40 is formed on the electron gun side surface of a shadow mask to an amount of coating of less than 0.2 mg/cm2 and also in that the electron reflection coat is formed by a sputtering method or a vapor deposition method. The coat thus formed becomes fine, and spontaneous peeling of the coat does not occur. Accordingly, good image quality can be obtained.
According to the fourth aspect of the present invention, an electronic tube is provided which is characterized in that an electron reflection coat is formed on the electron gun side surface of the shadow mask to an amount of coating of less than 2 mg/cm2, said electron reflection coat mainly comprising an element with an atomic number not lower than 40 and not higher than 69.
According to the fifth aspect of the present invention, an electronic tube is provided which is characterized in that an electron reflection coat is formed on the electron gun side surface of the shadow mask to an amount of coating of less than 0.2 mg/cm2, said electron reflection coat mainly comprising an element with an electron number not lower than 70.